Gene rearrangements in Ewing's sarcoma

Bioinformatic Analysis of Recurrent Genomic Alterations and Corresponding Pathway Alterations in Ewing Sarcoma

Ewing Sarcoma (ES) is an aggressive, mesenchymal malignancy associated with a poor prognosis in the recurrent or metastatic setting with an estimated overall survival (OS) of <30% at 5 years. ES is characterized by a balanced, reciprocal chromosomal translocation involving the EWSR1 RNA-binding protein and ETS transcription factor gene (EWS-FLI being the most common). Interestingly, murine ES models have failed to produce tumors phenotypically representative of ES. Genomic alterations (GA) in ES are infrequent and may work synergistically with EWS-ETS translocations to promote oncogenesis. Aberrations in fibroblast growth factor receptor (FGFR4), a receptor tyrosine kinase (RTK) have been shown to contribute to carcinogenesis. Mouse embryonic fibroblasts (MEFs) derived from knock-in strain of homologous Fgfr4G385R mice display a transformed phenotype with enhanced TGF-induced mammary carcinogenesis. The association between the FGFRG388R SNV in high-grade soft tissue sarcomas has previously been demonstrated conferring a statistically significant association with poorer OS. How the FGFR4G388R SNV specifically relates to ES has not previously been delineated. To further define the genomic landscape and corresponding pathway alterations in ES, comprehensive genomic profiling (CGP) was performed on the tumors of 189 ES patients. The FGFR4G388R SNV was identified in a significant proportion of the evaluable cases (n = 97, 51%). In line with previous analyses, TP53 (n = 36, 19%), CDK2NA/B (n = 33, 17%), and STAG2 (n = 22, 11.6%) represented the most frequent alterations in our cohort. Co-occurrence of CDK2NA and STAG2 alterations was observed (n = 5, 3%). Notably, we identified a higher proportion of TP53 mutations than previously observed. The most frequent pathway alterations affected MAPK (n = 89, 24% of pathological samples), HRR (n = 75, 25%), Notch1 (n = 69, 23%), Histone/Chromatin remodeling (n = 57, 24%), and PI3K (n = 64, 20%). These findings help to further elucidate the genomic landscape of ES with a novel investigation of the FGFR4G388R SNV revealing frequent aberration.

Imaging of pediatric bone tumors: A COG Diagnostic Imaging Committee/SPR Oncology Committee White Paper

Malignant primary bone tumors are uncommon in the pediatric population, accounting for 3%-5% of all pediatric malignancies. Osteosarcoma and Ewing sarcoma comprise 90% of malignant primary bone tumors in children and adolescents. This paper provides consensus-based recommendations for imaging in children with osteosarcoma and Ewing sarcoma at diagnosis, during therapy, and after therapy.

Systemic Treatment of Ewing Sarcoma: Current Options and Future Perspectives

Ewing sarcoma (ES) is an uncommon malignant neoplasm, mostly affecting young adults and adolescents. Surgical excision, irradiation, and combinations of multiple chemotherapeutic agents are currently used as a multimodal strategy for the treatment of local and oligometastatic disease. Although ES usually responds to the primary treatment, relapsed and primarily refractory disease remains a difficult therapeutic challenge. The growing understanding of cancer biology and the subsequent development of new therapeutic strategies have been put at the service of research in recurrent and refractory ES, generating a great number of ongoing studies with compounds that could find superior clinical outcomes in the years to come. This review gathers the current available information on the treatment and clinical investigation of ES and aims to be a point of support for future research.

Intraabdominal lesser sac metastasis from Ewing's sarcoma: An exceptional localization

Ewing's sarcoma/primitive neuroectodermal tumor is rare and aggressive with a poor prognosis. Intraabdominal metastases are an uncommon condition. Metastasis in the lesser sac is an exceptional occurrence. To the best of our knowledge, this location has not been described previously. We report a case of a 15-year-old patient treated for Ewing's sarcoma of the left arm 6 years back. She had developed a suspicious mass in the lesser sac 6 years following her primary tumor. The histopathologic exam revealed a tumor with "small round cells" that were positive for CD99, confirming the relapse of Ewing's sarcoma. The relapse was successfully managed with chemotherapy and surgery. Intraabdominal, extraintestinal masses in patients treated previously for Ewing's sarcoma should be considered as Ewing's sarcoma relapse in the differential diagnosis. We fully describe the management of this atypical relapse, with different components of clinical, radiological, and histological findings.

Risk factors for detectable metastatic disease at presentation in Ewing sarcoma - An analysis of the SEER registry

BACKGROUND

Ewing family of tumors (EFT) represents the second-most common primary bone malignancy in children and adolescents. Approximately 25% of patients have radiographically detectable metastatic disease at presentation and experience poorer five-year survival, yet risk factors for metastatic disease at presentation are poorly characterized. We sought to study patient characteristics associated with metastatic disease upon presentation for patients with EFT.

METHODS

We identified EFT cases in the Surveillance, Epidemiology, and End Results Program (SEER) registry from 2004 to 2012. Using univariate analyses and multivariable logistic regression, we explored the relationship between demographic and clinical factors and the presence of detectable metastatic disease at presentation.

RESULTS

Among 870 EFT cases, 35% (n = 304) presented with detectable metastatic disease. These patients were commonly older (>24 years: 28% vs 19%, p = 0.002) and had a primary tumor site in the axial skeleton (56% vs 44%, p < 0.001). After adjusting for all covariates, compared to patients <11 years, those >24 years old faced a two-fold increase in the odds of metastatic disease (OR = 1.99, 95% CI: 1.17-3.38). Axial (OR = 2.31, 95% CI: 1.58-3.37) and "other" (OR = 2.35, 95% CI: 1.15-4.81) tumor locations had more than twice the likelihood of presenting with metastatic disease, compared to extremity tumor sites. Increasing tumor size conferred up to a three-fold increase in odds of metastatic disease (pTrend <0.001).

CONCLUSIONS

Advanced age, axial tumor location, and increasing tumor size are associated with increased odds of detectable metastatic disease upon presentation with EFT. Although these characteristics are not modifiable, they provide objective factors that may inform patient counseling of metastatic risk.

Multimodality Treatment in Ewing's Sarcoma Family Tumors of the Maxilla and Maxillary Sinus: Review of the Literature

The Ewing sarcoma family of tumors (ESFT) encompasses a group of highly aggressive, morphologically similar, malignant neoplasms sharing a common spontaneous genetic translocation that affect mostly children and young adults. These predominantly characteristic, small round-cell tumors include Ewing's sarcoma of the bone and soft tissue, as well as primitive neuroectodermal tumors (PNETs) involving the bone, soft tissue, and thoracopulmonary region (Askin's tumor). Extraosseous ESFTs are extremely rare, especially in the head and neck region, where literature to date consists of sporadic case reports and very small series. We hereby present a review of the literature published on ESFTs reported in the maxilla and maxillary sinus region from 1968 to 2016.

Cancer stem cells in pediatric sarcomas

Sarcomas represent a clinically and biologically diverse group of malignant connective tissue tumors. Despite aggressive conventional therapy, a large proportion of sarcoma patients experience disease recurrence which will ultimately result in mortality. The presence of a unique population of cells, referred to as cancer stem cells (CSCs), have been proposed to be responsible for refractory responses to current chemotherapies as well underlying the basis for metastasis and relapse of disease – clinical corollaries to what has been termed the CSC hypothesis. The presence of CSCs have been suggested in a variety of hematologic and solid malignancies, and only more recently in sarcomas. Based on our current understanding of normal stem cell biology and evidence obtained from the study of malignant hematopoietic and solid tumors, researchers have identified candidate cell surface markers (CD133, CD117, Stro-1), biochemical markers (aldehyde dehydrogenase activity), and cytological characteristics (side population and spherical colony formation) that may identify putative sarcoma CSCs. In this review, we explore the current state of evidence that may suggest the existence of sarcoma CSCs. We present research in osteosarcoma, the Ewing’s sarcoma family of tumors, rhabdomyosarcoma, as well as other sarcoma subtypes to describe commonly used molecular and biochemical markers, as well as techniques, used in the identification, isolation, and characterization of candidate sarcoma CSCs. We will also discuss the current controversies and challenges that face research in sarcoma CSC.

Sequential Ewing's sarcoma and osteosarcoma

The sequential occurrence of two primary bone tumors, Ewing's sarcoma and osteosarcoma in the same patient at two different anatomical sites 5 years apart is rare. We report a case of 12-year-old boy who after treatment for Ewing's sarcoma of proximal fibula subsequently presented, 4 years later, with a high-grade fibroblastic osteosarcoma of the proximal humerus. The patient was also found to have a rare gene tranlocation t (7;22) instead of the more common t (11;22).

Establishment and characterization of a clonal human extraskeletal Ewing's sarcoma cell line, EES1

Ewing's sarcoma, a small round cell sarcoma arising in soft tissue as well as the bone, is one of the most malignant tumors in children and young adults. Few established cell lines of extraskeletal Ewing's sarcoma (EES) have been reported, which made it difficult to examine the biological features of EES. Therefore, we have established a new clonal cell line of EES. We report its morphological characters, results of chromosomal and immunohistochemical analysis. A piece of tumor obtained from the 18-year-old female patient with EES was xenografted in a nude mouse. In vitro subcultured cells were then obtained from this xenograft. A clonal cell line was subsequently established by limiting dilution and designated EES1. EES1 cells had a doubling time of 24 hours. In the xenografted tumor, the cells expressed vimentin, CD99 (MIC2), neuron specific enolase (NSE) and cytokeratin. The original tumor cells also expressed vimentin, CD 99, and NSE, but was negative for cytokeratin. The morphological and immunohistochemical features of this cell line established, except for cytokeratin expression, were consistent with those of the primary tumor. Cytogenetic analysis of EES1 revealed chromosomal translocation of t(11; 12)(q24;ql2). The chimeric fusion of the Ewing's sarcoma gene in band 22q12 with the Friend leukemia virus integration-1 gene in band 11q24 was also demonstrated. Fluorescence in situ hybridization further confirmed the presence of translocation involving the Ewing's sarcoma gene in both the primary tumor and EES1 cells. In conclusion, we have established a human EES cell line EES1, which will provide a useful model for studying various aspects of human EES.

Ewing's sarcoma and primitive neuroectodermal family of tumors

Ewing's sarcoma (ES) initially was believed to be of perivascular endothelial origin. The Ewing's sarcoma family of tumors (EFT) includes ES of bone (ESB), extraosseous ES (EES), peripheral primitive neuroectodermal tumor of bone (pPNET), and malignant small-cell tumor of the thoracopulmonary region, or Askin's tumor, all of which are now known to be neoplasms of neuroectodermal origin. The degree of neuronal differentiation has been used for histopathologic subclassification of the EFT as classical ES (ESB or EES), which is characterized by minimal evidence of neural differentiation, and pPNET, which displays evidence of neural differentiation by standard microscopy, electron microscopy, or immunohistochemistry. Because the behavior, prognosis, and treatment appear to be similar for all subsets of EFT, this histopathologic subclassification may not be clinically significant, though some debate remains whether neural differentiation predicts for inferior outcome.

G-CSF induces stabilization of ETS protein Fli-1 during myeloid cell development

Granulocyte colony-stimulating factor (G-CSF) is a growth factor that regulates the production and function of neutrophils. G-CSF has been used to treat neutropenia in neonates, pediatric cancer patients, and patients undergoing stem cell transplantation. The regulation of transcription factors mediating G-CSF activity has not been well characterized. The goal of this study was to examine the regulation of the ETS binding protein, Friend leukemia integration site 1 (Fli-1), in myeloid cells treated with G-CSF. Fli-1 has oncogenic properties in humans and mice, and plays a role in vascular and hematopoietic cell development. We previously reported that Fli-1 and the serum response factor bind at adjacent sites within the serum response element-1 of the early growth response gene-1 promoter in the murine myeloid leukemic cell line, NFS60. We also identified that Fli-1 DNA binding increased in G-CSF-treated cells compared with untreated cells. To determine whether the change in binding activity is due to increased Fli-1 transcription or protein stability, we examined endogenous Fli-1 expression in G-CSF-treated or -untreated NFS60 cells. Our results demonstrated that levels of Fli-1 protein, but not RNA, were higher in extracts from cells treated with G-CSF. The increase in Fli-1 protein was also dependent on protein synthesis. Finally, we showed that the half-life of Fli-1 is prolonged in G-CSF-treated cells compared with control-treated cells. These results suggest that G-CSF induces stabilization of Fli-1 protein in myeloid cells, thus proposing a novel mechanism by which hematopoietic growth factors regulate transcription factors.

Adenovirus-mediated p53 gene therapy in pediatric soft-tissue sarcoma cell lines: sensitization to cisplatin and doxorubicin

Sarcomas, or tumors of connective tissue, represent roughly 20% of childhood cancers. Although the cure rate for sarcomas in general has significantly improved in the last 10 years, there continue to be subgroups that are difficult to treat. High-grade or metastatic soft-tissue sarcomas and rhabdomyosarcomas (RMS) of the extremities remain therapeutic challenges and their prognosis is often poor. The future of sarcoma therapy will likely include molecular approaches including gene/protein expression profiling and gene-based therapy. Most sarcomas harbor defects in the p53 or pRb pathways. The tumor suppressor p53 is central to regulation of cell growth and tumor suppression and restoring wild-type p53 function in pediatric sarcomas may be of therapeutic benefit. Studies with adenoviral-mediated p53 gene transfer have been conducted in many cancer types including cervical, ovarian, prostatic and head and neck tumors. Studies of this approach, however, remain limited in pediatric cancers, including sarcomas. Using three viral constructs containing cDNA for wild-type p53, mutant p53 (C135S) and lacZ, we studied the effect of adenoviral-mediated gene therapy in four pediatric sarcoma cell lines, RD and Rh4 (RMS), Rh1 (Ewing's sarcoma) and A204 (undifferentiated sarcoma). Using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, we have shown a dose-dependent decrease in cell viability 72 h post-treatment that occurs with Ad-wtp53 but not with Ad-mutp53. Cells treated with Ad-wtp53 show upregulation of the p53 downstream targets, p21(CIP1/WAF1) and bax. Growth curves demonstrate suppression of cell growth over a period of 4 days and cells treated with Ad-wtp53 demonstrate a significant increase in sensitivity to the chemotherapeutic agents, cisplatin and doxorubicin. Our results indicate that restoration of wild-type p53 function in pediatric sarcoma cells could provide a basis for novel approaches to treatment of this disease.

The Ews/Fli-1 fusion gene switches the differentiation program of neuroblastomas to Ewing sarcoma/peripheral primitive neuroectodermal tumors

Neuroblastoma (NB) and the Ewing sarcoma (ES)/peripheral primitive neuroectodermal tumor (PNET) family are pediatric cancers derived from neural crest cells. Although NBs display features of the sympathetic nervous system, ES/PNETs express markers consistent with parasympathetic differentiation. To examine the control of these differentiation markers, we generated NB x ES/PNET somatic cell hybrids. NB-specific markers were suppressed in the hybrids, whereas ES/PNET-specific markers were unaffected. These results suggested that the Ews/Fli-1 fusion gene, resulting from a translocation unique to ES/PNETs, might account for the loss of NB-specific markers. To test this hypothesis, we generated two different NB cell lines that stably expressed the Ews/Fli-1 gene. We observed that heterologous expression of the Ews/Fli-1 protein led to the suppression of NB-specific markers and de novo expression of ES/PNET markers. To determine the extent of changes in differentiation, we used the Affymetrix GeneChip Array system to observe global transcriptional changes of genes. This analysis revealed that the gene expression pattern of the Ews/Fli-1-expressing NB cells resembled that observed in pooled ES/PNET cell lines and differed significantly from the NB parental cells. Therefore, we propose that Ews/Fli-1 contributes to the etiology of ES/PNET by subverting the differentiation program of its neural crest precursor cell to a less differentiated and more proliferative state.

Inhibition of anchorage-independent growth of transformed NIH3T3 cells by epithelial protein lost in neoplasm (EPLIN) requires localization of EPLIN to actin cytoskeleton

Epithelial protein lost in neoplasm (EPLIN) is a cytoskeleton-associated protein characterized by the presence of a single centrally located lin-11, isl-1, and mec-3 (LIM) domain. We have reported previously that EPLIN is down-regulated in transformed cells. In this study, we have investigated whether ectopic expression of EPLIN affects transformation. In untransformed NIH3T3 cells, retroviral-mediated transduction of EPLIN did not alter the cell morphology or growth. NIH3T3 cells expressing EPLIN, however, failed to form colonies when transformed by the activated Cdc42 or the chimeric nuclear oncogene EWS/Fli-1. This suppression of anchorage-independent growth was not universal because EPLIN failed to inhibit the colony formation of Ras-transformed cells. Interestingly, the localization of EPLIN to the actin cytoskeleton was maintained in the EWS/Fli-1- or Cdc42-transformed cells, but not in Ras-transformed cells where it was distributed heterogeneously in the cytoplasm. Using truncated EPLIN constructs, we demonstrated that the NH(2)-terminal region of EPLIN is necessary for both the localization of EPLIN to the actin cytoskeleton and suppression of anchorage-independent growth of EWS/Fli-1-transformed cells. The LIM domain or the COOH-terminal region of EPLIN could be deleted without affecting its cytoskeletal localization or ability to suppress anchorage-dependent growth. Our study indicates EPLIN may function in growth control by associating with and regulating the actin cytoskeleton.

Ewing's sarcoma/primitive neuroectodermal tumor of the chest wall

Ewing's sarcoma/primitive neuroectodermal tumor is the most common tumor of the chest wall in children and adolescents. It is extremely malignant with a high frequency of both metastatic spread and of local recurrence. Cure requires intensive therapy to control both distant and local disease. Surgery and high-dose radiotherapy can achieve equivalent local control; however, radiation is associated with the additional morbidities of second malignancy and a significant adverse impact on both cardiac and pulmonary function. The optimal therapeutic sequence is initial biopsy followed by induction chemotherapy with subsequent resection of the primary tumor. This approach will achieve the lowest incidence of tumor present at the margins of resection and, hence, need for postoperative radiotherapy. The chest wall is a rare site for tumors in children and adolescents. In a series reported from St Jude's Children's Research Hospital, chest wall tumors constituted only 1.8% of the solid childhood tumors. They are primarily mesenchymal in origin and the Ewing's sarcoma/primitive neuroectodermal tumors (PNET) predominate. This report concentrates on the later tumors. They are recognized to be extremely malignant, and cure in those who present with metastatic disease is very difficult to achieve. Recent advances in our understanding of their cytogenetic basis and optimal treatment are presented.

EWS fli-1 antisense nanocapsules inhibits ewing sarcoma-related tumor in mice

EWS Fli-1, a fusion gene resulting from a t(11;22) translocation is found in 90% of both Ewing's sarcoma and primitive neuroectodermal tumor (PNET). In the present study, we show that recently developed polyisobutylcyanoacrylate nanocapsules with an aqueous core were able to encapsulate efficiently high amounts of phosphorothioate oligonucleotides (ODN) directed against EWS Fli-1 chimeric RNA. Release of these ODN in serum medium was shown to be biphasic which was explained by the presence of two types of nanocapsules able to release ODN with different kinetics. In addition, nanocapsules were found to provide protection of these oligonucleotides from the degradation in serum. These ODN nanocapsules permitted to obtain inhibition of Ewing sarcoma-related tumor in mice after intratumoral injection of a cumulative dose as low as 14.4 nanomoles. This new type of non viral vector shows great potential for in vivo administration of oligonucleotides.

Lovastatin induces apoptosis in a primitive neuroectodermal tumor cell line in association with RB down-regulation and loss of the G1 checkpoint

To develop a new approach to the treatment of primitive neuroectodermal tumors we evaluated the effect of the HMG-CoA reductase inhibitor lovastatin on the Ewing's sarcoma cell line CHP-100. Lovastatin induced neural morphology and markers including neuron-specific enolase and neurofilament protein. The acquisition of neural morphology required new mRNA synthesis, and cDNA microarray analysis confirmed that lovastatin altered the program of gene expression. After morphologic differentiation the cells underwent rapidly progressive apoptosis. In normal development of neuronal progenitors, differentiation signals trigger p21WAF1 accumulation, RB hypophosphorylation, enhanced RB-E2F-1 association, and G1 arrest, and these events have been shown to protect from apoptosis. In contrast, in the Ewing's sarcoma cells lovastatin triggered differentiation without causing cell cycle arrest: p21WAF1 was not induced, RB remained hyperphosphorylated, and RB protein expression and RB-E2F-1 association were markedly downregulated, suggesting that loss of an RB-regulated G1 checkpoint promoted apoptosis. Consistent with this hypothesis, adenoviral p21WAF1 decreased DNA synthesis and partially protected from lovastatin-induced cytotoxicity. The data demonstrate a new model for examining the genetic regulation of cell fate in a neural progenitor tumor and suggest a new approach to the treatment of this neoplasm.

Divergent Ewing's sarcoma EWS/ETS fusions confer a common tumorigenic phenotype on NIH3T3 cells

Ewing's sarcomas express chimeric transcription factors resulting from a fusion of the amino terminus of the EWS gene to the carboxyl terminus of one of five ETS proteins. While the majority of tumors express EWS/FLI1 fusions, some Ewing's tumors contain variant chimeras such as EWS/ETV1 that have divergent ETS DNA-binding domains. In spite of their structural differences, both EWS/ETS fusions up regulate EAT-2, a previously described EWS/FLI1 target gene. In contrast to EWS/FLI1, NIH3T3 cells expressing EWS/ETV1 cannot form colonies in soft agar though coexpression of a dominant negative truncated ETV1 construct attenuates EWS/FLI1 mediated anchorage independent growth. When EWS/ETV1 or EWS/FLI1 expressing NIH3T3 cells are injected into SCID mice, tumors form more often and faster than with NIH-3T3 cells with empty vector controls. The tumorigenic potency of each EWS/ETS fusion is linked to its C-terminal structure, with the FLI1 C-terminus confering a greater tumorigenic potential than the corresponding ETV1 domain. The resulting EWS/ETV1 and EWS/FLI1 tumors closely resemble each other at both a macroscopic and a microscopic level. These tumors differ greatly from tumors formed by NIH3T3 cells expressing activated RAS. These data indicate that in spite of their structural differences, EWS/ETV1 and EWS/FLI1 promote oncogenesis via similar biologic pathways.

Vasoactive intestinal peptide (VIP) and VIP receptors: gene expression and growth modulation in medulloblastoma and other central primitive neuroectodermal tumors of childhood

Vasoactive intestinal peptide (VIP) is a neuromodulator and growth regulator in the developing nervous system. We analyzed 10 primitive neuroectodermal tumor (PNET) cell lines, 29 central PNET (cPNET) and 17 tumors of the Ewing's sarcoma/peripheral PNET family (ESFT) using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern hybridization. Each of the 10 cell lines and 86.2% of cPNET expressed mRNA for VIP receptor 1 (VIPR1) compared to 52.9% of ESFT. VIPR2 was expressed in 75.8% of cPNET, in 28.6% of ESFT and in all 10 cell lines. cPNET demonstrated high-affinity binding of 125I-VIP on quantitative autoradiography and in competitive binding assays. VIP inhibited tumor cell proliferation in a dose-dependent manner in 5 of 7 PNET cell lines. We conclude that VIPR1 and VIPR2 are highly expressed in cPNET and demonstrate that VIP is a growth modulator in these tumors.

Pediatric bone tumors

Although osteosarcoma and Ewing's sarcoma are quite rare, they are the only primary skeletal malignancies that occur with any regularity in children. The evaluation, diagnosis, and management of skeletal neoplasia are reviewed using these two diseases as the focus of discussion. Radiographic imaging, biopsy approaches, diagnostic considerations, and therapeutic management are explained. Demographics and pathophysiology of osteosarcoma and Ewing's sarcoma are explored in more depth.

Intraabdominal desmoplastic small round cell tumor with EWS/ERG fusion transcript

This report describes an intraabdominal small cell tumor in a 37-year-old woman, with clinical, topographic, and morphologic features highly suggestive of the desmoplastic small round cell tumor. Immunohistochemical analysis revealed a polyphenotypic profile consistent with this tumor--positivity for keratin, epithelial membrane antigen, neuron-specific enolase, vimentin, and desmin--but, in addition, a strong membranous immunoreactivity for CD99 (MIC2 protein). Reverse transcription polymerase chain reaction revealed a EWS/ERG fusion transcript characteristic of the Ewing's sarcoma/peripheral primitive neuroectodermal tumor group of tumors, rather than the EWS/WT1 chimeric transcript typical of the desmoplastic small round cell tumor. This is the third report of a hybrid tumor with features of the desmoplastic small round cell tumor and Ewing's sarcoma/peripheral primitive neuroectodermal tumor, and the first one with the EWS/ERG fusion gene. Our case shows the existence of some overlap between these two groups of tumors, which are considered to be histogenetically different, and the need for further studies of molecular characterization of small cell tumors, especially in those with atypical morphologic or immunohistochemical features.